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Shoham et al. Journal of Cardiothoracic Surgery 2010, 5:39
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CASE REPORT
© 2010 Shoham et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License ( which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
Case report
Mechanical ventilation and the total artificial heart:
optimal ventilator trigger to avoid post-operative
autocycling - a case series and literature review
Allen B Shoham*
1
, Bhavesh Patel
2
, Francisco A Arabia
3
and Michael J Murray
1
Abstract
Many patients with end-stage cardiomyopathy are now being implanted with Total Artificial Hearts (TAHs). We have
observed individual cases of post-operative mechanical ventilator autocycling with a flow trigger, and subsequent loss
of autocycling after switching to a pressure trigger. These observations prompted us to do a retrospective review of all
TAH devices placed at our institution between August 2007 and May 2009. We found that in the immediate post-
operative period following TAH placement, autocycling was present in 50% (5/10) of cases. There was immediate
cessation of autocycling in all patients after being changed from a flow trigger of 2 L/minute to a pressure trigger of 2
cm H
2
O. The autocycling group was found to have significantly higher CVP values than the non-autocycling group (P =
0.012). Our data suggest that mechanical ventilator autocycling may be resolved or prevented by the use of a pressure
trigger rather than a flow trigger setting in patients with TAHs who require mechanical ventilation.
Background

In 2006, end-stage cardiomyopathy was the primary
cause of death for almost 60,000 Americans[1]. Trans-
plantation would have prevented many of these deaths;
however, only 3205 patients worldwide received trans-
planted hearts in 2006[2]. Since the publication of the
REMATCH study, [3] patients with end-stage cardiomyo-
pathy have increasingly received total artificial hearts
(TAHs) as a bridge to cadaveric cardiac transplantation,
with surgeons currently implanting third-generation
devices[4]. We must be diligent in maintaining our
knowledge of these devices, as well as our skills in provid-
ing care to patients with TAHs.
After they have had a TAH implanted, patients typically
remain tracheally intubated and mechanically ventilated
for several days to weeks. While caring for such patients
in our institution, we noticed that many developed post-
operative autocycling of the mechanical ventilator when a
flow trigger was used to initiate breaths (Figure 1), which
subsequently stopped when we switched the ventilator to
a pressure trigger (Figure 2). Autocycling refers to the
inappropriate triggering of a ventilator assisted breath in
the absence of a spontaneous patient effort. These obser-
vations piqued our curiosity regarding the frequency of
this occurrence and precipitated the initiation of this ret-
rospective chart review.
Methods
Following institutional review board approval, we
reviewed the computerized medical records of all
patients with a TAH placed at our institution between
August 2007 and May 2009. We created a database using

Excel (Microsoft, Redmond, WA) and recorded the cen-
tral venous pressure (CVP) while the patients were
mechanically ventilated, the positive end expiratory pres-
sure (PEEP), mode of ventilation, body mass index (BMI),
TAH rate, and both the set and actual respiratory rate
while the patients' ventilators were set for both flow and
pressure triggering. A 1-tailed equal variance student t
test was done to compare the BMI and CVP values of the
autocycling group and the non-autocycling group.
The medical records of 10 patients were identified for
review (Table 1). All patients were older than 40 years of
age; exact ages have not been included in this report
because of the need for patient confidentiality. The artifi-
cial heart device used in all patients was the SynCardia
CardioWest (Tucson, AZ). The mechanical ventilator
* Correspondence:
1
Department of Anesthesiology, Mayo Clinic Arizona, 5777 East Mayo
Boulevard, Phoenix, Arizona 85054, USA
Full list of author information is available at the end of the article
Shoham et al. Journal of Cardiothoracic Surgery 2010, 5:39
/>Page 2 of 4
used in all patients was the Puritan Bennett 840 (Pleasan-
ton, CA).
Results
Data from all 10 patients (Table 1) shows that 8 had a flow
trigger of 2 L/minute as the initial ventilator setting, with
a change in all 8 to a pressure trigger of 2 cm
H
2

O within
the first 48 hours after TAH placement. One patient was
kept on a flow trigger of 2 L/minute until extubation
without any autocycling noted, and another patient was
kept on a pressure trigger of 2 cm
H
2
O until extubation
without any autocycling recorded.
Five of the 10 patients developed autocycling of the
ventilator, but autocycling ceased immediately in all of
these patients when their ventilator settings were
changed from a flow trigger of 2 L/minute to a pressure
trigger of 2 cm
H
2
O. There were no documented changes
in the patients' levels of sedation, mentation, or neuro-
muscular blockade when these changes were made.
Discussion
A search of PubMed using the terms ventilation and arti-
ficial heart and autocycling and artificial heart on May
23, 2009, did not reveal any publications regarding auto-
cycling associated with TAH devices, nor did we find a
description of optimal mechanical ventilator settings for
patients who have received a TAH or strategies to post-
operatively manage the ventilators of such patients.
Potential consequences of mechanical ventilator auto-
cycling include respiratory alkalosis, barotrauma, patient
ventilator dysynchrony, and over use of sedative medica-

tions[5,6]. In 1 of our patients, the presence of autocy-
cling resulted in evaluation and work-up for central
hyperventilation syndrome. Such an evaluation typically
includes invasive testing that could be potentially harmful
to the patient.
Flow- and pressure-triggered mechanical ventilator
modes are designed to allow and assist with spontaneous
ventilation. In a pressure-trigger mode, the patient's
inspiratory effort is recognized when the airway pressure
decreases below the baseline level of PEEP by the set trig-
ger sensitivity (2 cm
H
2
O in our cases). Once this occurs,
the ventilator delivers an assisted breath.
In a flow-trigger mode using the Puritan Bennett 840
mechanical ventilator, the baseline continuous expiratory
flow is set at 1.5 L/min greater than the set flow trigger (2
L/min in our case), resulting in a continuous expiratory
flow of 3.5 L/min. The patients' inspiratory effort is rec-
ognized as a drop in expiratory flow by the set trigger
sensitivity, consequently resulting in a ventilator-assisted
Figure 1 TAH induced autocycling is present with an actual RR of
28 using a flow trigger.
Actual RR
Triggered Breath
StRR
Flow
S
e

t

RR
Trigger
Figure 2 Autocycling is absent with the use of a pressure trigger
as the actual RR = set RR of 16.
Actual RR
StRR
Pressure
Ti
S
e
t

RR
T
r
i
gge
r
Shoham et al. Journal of Cardiothoracic Surgery 2010, 5:39
/>Page 3 of 4
breath. In our case, this would occur when expiratory
flow is less than 1.5 L/min.
Use of a flow trigger has been shown to decrease the
inspiratory work of breathing in patients with chronic
obstructive pulmonary disease and intrinsic PEEP
(iPEEP)[7]. In the case of iPEEP, the patient would have to
produce a greater negative pressure to overcome the dif-
ference between intrinsic and circuit PEEP. However,

with newer ventilator programming, the inspiratory work
of breathing is similar between flow and pressure trigger
modes[8,9].
Any device that alters resistance from the alveolus to
the sensor at the y-piece, such as gas leaks from ventilator
circuits, leaks in the cuff of the tracheal tube[5,10]. a heat
moisture exchanger, [6] and an in-line catheter, can be a
source of ventilator autocycling[11]. Cardiac oscillations
are another well-known source of autocycling and have
been described in patients in the ICU and during general
anesthesia[12]. Cardiac oscillations leading to autocy-
cling in patients who have undergone cardiac surgical
procedures has been shown to be relatively common with
flow-trigger settings, particularly in patients who have
large cardiac outputs, large heart size, low respiratory
system resistance, and an elevated CVP[13]. The differ-
ences we have observed in incidence of autocycling may
not only reflect the method of triggering (flow vs. pres-
sure), but also the sensitivity of the trigger used as the
more sensitive the setting, the more likely autocycling
will occur; flow-triggering has been shown to be particu-
larly sensitive to circuit leaks[5,6,10,11].
The autocycling group in our case series did have sig-
nificantly higher CVP values than the non-autocycling
group (P = 0.012), though we can not draw any causative
conclusions with this post hoc data. An elevated CVP
may reflect decreased intra-thoracic compliance, thereby
increasing transmitted pressure changes to the airway
with resultant autocycling. The elevated CVP may also
simply be a consequence of mechanical ventilator autocy-

cling rather than a cause.
TAH oscillations induce significant pulmonary volume
displacement as there are large pneumatic pressure
changes for each beat[14,15]. A patient with post-opera-
Table 1: Case Series Data
Patient Mode of ventilation CVP BMI RRactual/set with flow
trigger
RRactual/set with pressure
trigger
TAH rate PEEP
Autocycling group
1 ACV 20 27.5 37/24 26/26 101 5
2 SIMV + PS 21 28.7 38/6 10/10 123 5
3 SIMV + PS 22 39.7 16/12 18/18 115 6
4 SIMV + PS 20 25.9 37/12 12/12 131 5
5 SIMV + PS 19 23.6 27/12 12/12 115 16
Nonautocycling group
6 SIMV + PS 18 31.2 10/10 110 8
7 SIMV + PS 7 32.3 18/18 30/30 110 25
8 SIMV + PS 15 32.3 10/10 125 5
9 SIMV + PS 19 25.8 18/12 18/12 120 5
10 SIMV + PS 10 30.8 14/10 12/10 110 5
ACV refers to assist control ventilation; SIMV, synchronized intermittent mechanical ventilation; PS, pressure support; CVP, central venous
pressure; BMI, body mass index; RR, respiratory rate; TAH, total artificial heart; PEEP, positive end expiratory pressure.
Shoham et al. Journal of Cardiothoracic Surgery 2010, 5:39
/>Page 4 of 4
tive respiratory failure after Jarvik-7 TAH placement
showed significant lung displacement during apnea[15].
In fact, this patient's cardiac oscillations were large
enough for sustained alveolar ventilation with an arterial

pCO
2
of 61 after one hour of total apnea. The Jarvik-7
TAH is the most recent structural cousin to our current
CardioWest TAH device.
Why is it that autocycling occurred in 50% of our
patients with a flow trigger but not with a pressure trig-
ger? Modern mechanical ventilators maintain PEEP and
compensate for changes in circuit pressure by adjusting
the exhalation valve with an active microprocessor con-
trol throughout the expiratory period[16]. The micropro-
cessor actively adjusts the expiratory valve to maintain a
set PEEP, ultimately leading to subsequent changes in cir-
cuit flow. The result is that pressure is maintained at the
expense of a change in flow. The CardioWest TAH initi-
ates very large intra-thoracic pressure changes that, by
definition, are transmitted to the airway. With a pressure
trigger, PEEP maintenance may compensate for the TAH-
induced pressure changes prior to a breath being trig-
gered. With a flow trigger the microprocessor once again
compensates for the pressure change induced by the
cycling of the TAH. This compensation, leads to pressure
maintenance at the expense of a change in flow, which
may then trigger an autocycled breath if timed correctly.
Conclusion
In summary, autocycling of the mechanical ventilator
occurred in 50% of patients who had received TAHs with
the use of a flow trigger ventilator setting. Autocycling
was resolved in all these patients by changing from a flow
trigger to a pressure trigger ventilator setting. Mechanical

ventilator PEEP maintenance maintains pressure at the
expense of altered flow, ultimately leading to autocycling
in the case of a flow trigger. Given the frequency of auto-
cycling in the ICU, this information may be applicable to
other patients who are mechanically ventilated. Because
advanced ventilator software has significantly diminished
differences in inspiratory work of breathing, physicians
may consider using a pressure trigger as an initial ventila-
tor mode, or switching to this mode in patients suspected
of, or at high risk for autocycling.
Competing interests
The authors declare that they have no competing interests.
Authors' contributions
AS reviewed the literature, drafted and completed the manuscript. BP and MM
assisted in drafting and reviewing the manuscript. FA performed surgical inter-
ventions and reviewed the manuscript. Both FA and BP participated in post-
operative management of patients studied. All authors read and approved the
final manuscript.
Acknowledgements
We would like to thank Catherine F. Murray for generously volunteering her
time to assist with drafting, editing and formatting this manuscript.
Author Details
1
Department of Anesthesiology, Mayo Clinic Arizona, 5777 East Mayo
Boulevard, Phoenix, Arizona 85054, USA,
2
Department of Critical Care, Mayo
Clinic Arizona, 5777 East Mayo Boulevard, Phoenix, Arizona 85054, USA and
3
Department of Cardiothoracic Surgery, Mayo Clinic Arizona, 5777 East Mayo

Boulevard, Phoenix, Arizona 85054, USA
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doi: 10.1186/1749-8090-5-39
Cite this article as: Shoham et al., Mechanical ventilation and the total artifi-

cial heart: optimal ventilator trigger to avoid post-operative autocycling - a
case series and literature review Journal of Cardiothoracic Surgery 2010, 5:39
Received: 21 January 2010 Accepted: 17 May 2010
Published: 17 May 2010
This article is available from: 2010 Shoham et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Journal of Cardiothoracic Surgery 2010, 5:39